Electroless Ni coatings for the improvement of wear resistance of bearings for lightweight rotary gear pumps

The possibility of improving the performances of current aluminium alloys in the bearings region of lightweight external gear pumps has been investigated. Two different electroless Ni-based coatings, one containing high percentages of P (10-14%) and the other modified with the addition of 25 wt% PTFE micrometric spheres, deposited on 2011 Al alloy, were characterised by scratch test and ball-on-disc tests. Comparison with an antifriction Sn-containing Al-alloy was performed. The PTFE-containing coating presents the lowest wear rate and friction against steel. However, the presence of PTFE spheres and the hardness mismatch with the substrate tends to favour tensile cracking of the coating.